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The tentacles spoke to me, asked what I wanted to be. To be weak I said, to be flawed, vulnerable. To perceive weakness in others not to exploit but to protect. To be a guide, to be a teacher.
~ Korosensei's goal.


Korosensei was the homeroom teacher for Class 3-E of Kunugigaoka Junior High School, and the central character and main antihero of Assassination Classroom. He claimed to be responsible for creating the permanent crescent moon and said that he planned to destroy the earth after "teaching" Class 3-E for a year.

Prior to being a teacher, he was the master assassin known as the 1st "Deity of Death ".

Appearance

Korosensei had the appearance of a yellow bipedal octopus. He was about three meters tall and possessed a large, bulbous head with a large smile and small, beady eyes. He used two feelers as arms, with two fingers each, and utilized the rest of his tentacles to walk with. According to Korosensei himself, his nostrils are so small yet when discovered, it seemed that he had four eyes.

Korosensei wore a black academic dress, a small black square academic cap with a yellow tassel, and a large black tie with a yellow crescent-shaped moon on it.

He seemed to make a habit of dressing in formal clothing. After being taken prisoner by Yanagisawa, he was put in patients' scrubs until his escape.

Personality

It was revealed that he was raised in an environment "where everybody could easily betray one another to the point that one could only trust oneself". Through these hardships, he decided to become an assassin in order to survive. Despite he gained an apprentice, he only saw him as a tool for his goals, which caused the latter to finally betraying his master.

However, after meeting to Aguri Yukimura, he finally knew what compassion really was- becoming much more kind and compassionate. According to Aguri, if he was born in a peaceful country, his personality would be "someone a little perverted, with a good head but a few screws loose, petty about small things, and also a lot stubborn... or something like that." He has/would have "a gentle smile not just for business, but because he is a gentle person himself." This prediction happens to reflect his personality which became forefront after he answered the tentacles.

When first introduced, Korosensei was a jovial individual who demanded absurd and seemingly mundane requests despite claiming he would be the cause of the planet's destruction in a year. He was also rather kind to others in general and could switch from silly and childish to serious on the fly. According to Nagisa, Korosensei also was unintentionally petty at others at times and loved gossip, both traits heavily noted through the series.

From time to time pieces of his old personality as The Reaper were visible such as when Terasaka tried to sacrifice Nagisa to kill Korosensei and Korosensei menacingly threatened all of their families if they tried another self-harming attempt like that. In that moment he resorted to his old method of teaching through fear. As the series progresses his character development renders him more and more capable of true empathy and learning to use that empathy to teach lessons instead of through fear and reward like he had with his first student.

Korosensei deeply cared for his students' emotional and physical well-being and would lose his temper whenever any of them were put in danger, even by one another. On the annual school trip to Kyoto, a few of his students were assaulted/kidnapped by a gang of high schoolers hidden in an alley. After searching the entire area painstakingly, he infiltrated the abandoned building where two kidnapped students were being held at and single-handedly beat up all of the high schoolers and scaring them away.

One of Korosensei's attributes was the fact that he was able to connect to each student individually, being an objective, empathic, and observant person who will do almost anything to help his students. This was the reason why all the students respect him despite the fact that he was going to blow up the Earth in a year. Taking care of each student's needs, Korosensei would sometimes be piqued by a student's current problems or interests and would try his best to guide the student along or solve it for them.

Korosensei loved sweets almost to extreme cases, and was also shown to be a very perverted character, a trait he shares with his student Okajima. This characteristic was revealed to be the side effect of the experimentation which made him unable to hide his true feelings.

Etymology

His name, Korosensei, is a combination of the words 殺せない (koro, 殺せない) which means "unkillable" and the word 先生 (sensei, 先生) which means teacher. It was given to him by Kaede Kayano.

Powers and Abilities

Antimatter Physiology: Due to the human experiments of produing antimatter in a living body by Shiro, Korosensei's entire appearance is an octopus-like creature with multiple tendrils that are his tentacles. Anything aside Anti-Sensei Weapons will be immune to him. It is initially believed that he will self-destruct by the time of Class E's graduation; however it has since been proven that the chances are minuscule at best

  • Protective Coloring: Korosensei can change any color for his skin and it is used for his disguises and camouflages. It is also the principle of the faces which represents his moods. Since it is only apply on his skin, to fully use the ability Korosensei must be fully naked. Although when he is blushing, the coloring won't cover the blushes on his face.
  • Mucus: The standard trait of an Antimatter organism, the mucus that Korosensei has varied uses for support purposes, such as waterproofing, cleansing, adhesive and the replacement of tears.
    • Liquefaction: After he drank the 4th poison made by Manami Okuda, Korosensei developed an ability to control his fluidity. He can morph into a mass of mercury-like slime. In cost of his massive body and tentacles, Korosensei can fit through any space while retaining most of his abilities. It is unknown that if there are any demerits to over use this ability.
  • Absolute Defense: Another trump card never used until the Okinawa trip, Korosensei can shrink his body into a sphere and the remaining energy from the transformation hardens as a crystallized second layer over his spherical body, making him impervious to harm. After twenty four hours, the external shell liquefies and he will slowly absorb energy over a period of time until he fully regenerates. The only drawback to this in the span of a day, he is rendered immobile and is susceptible to being carried around. The only mechanism might be able to breakthrough this sphere is Lance of the Heavens.
    • Energy Laser: An ability developed from the Absolute Defense. Korosensei can tap a portion of his inner energy to his tentacles in order to create a laser blast from it. It is capable to annihilate the Anti-Sensei Cloth and blast off anything else with scratches barely left over.
  • Molting: A once-a-month occurrence, Korosensei can shed his old skin and use it as a protective membrane either on himself or another individual, protecting them from being hurt even from military-grade explosives. Afterwards, his reaction speed may slow temporarily but he is still fast enough to dodge the assassins of 3-E.
  • Regeneration: If one or more of his tentacles are maimed, Korosensei can regenerate the severed limb like a lizard regenerating its tail. However, this leaves his stamina weakened as his reaction speed is dampened, albeit not enough to topple the teacher.
    • Surgery Skills: After he was unable to save Aguri from fatal wounds, he start learn about medical operation and surgery methods which he first apply it on Azusa to remove her brain tumour without damaging her. Later, he use it to heal and revive Akari (Kayano) from fatal wounds that was caused by God of Death and Yanagisawa after surgery has been completed. Like his Regeneration and Molting, the surgery also can weaken his stamina, which sometimes need to replenish is stamina during the process of the surgery.
  • Superhuman Speed: Korosensei can travel up to the speed of Mach 20. His normally soft and jelly-like head hardens under immense pressure as a process known as the dilatancy phenomenon, which presumably lowers his wind resistance, allowing him to reach inhuman speeds. The only known objects to surpass this are space shuttles which is used for space launch which reaches the speed of Mach 23 and other Advanced-Antimatter Organisms.
    • Superhuman Reflexes: Korosensei can react and dodge multiple fires of Anti-Sensei bullets and move away from any harm. His reflexes also allow him to react fast enough to catch or deflect any flying projectile in mid-air using what he has on hand such as handkerchief or even a chalk. Another example of this is when facing off against Asano Gakuho, he was able to open a test book, solve a denoted question on a small slip of paper and close the book without the explosive contained in the book detonating. Plus, he is also fast enough to molt and toss his protection skin over the principal when a normal grenade detonated point-blank in his face.
    • Speed Replication: Korosensei's amazing speed allows him to seemingly copy himself dozens of times using after-imagery. Not only can each individual after-image maintain a task for extended periods of time, but Korosensei's "speed copies" are all capable of taking on widely-different tasks both individually and simultaneously without confusing themselves. This technique was primarily used by Korosensei to teach all of Class 3-E one-on-one when a difficult test approached, allowing Korosensei to work with each student separately to work on their problem subjects.
  • Superhuman Senses: Korosensei's sensory perceptions are paramount, and can detect even the most minuscule of changes in temperature, light, sound, and smell. Despite having no visible ears or nose, Korosensei has proven to be able to hear things no normal human can pick up on, as well as detect the most minor of aromas, which aided him greatly in evading the assassination attempts of Class 3-E. Korosensei is especially talented in identifying people by their smell, as well as certain materials (such as explosives and poisons). His eyes are also quite keen, and can keep track of objects going thousands of miles per hour without difficulty, as well as detect the slightest of movements that occur quicker than the blink of an eye.
  • Superhuman Digestion: Korosensei can digest anything aside Anti-Sensei weapons His teeth can crush any hard materials. Whether he eats something or it enters his body, he can either molten the food first then eject it, or it will just be digested. Although it is not guaranteed that Korosensei will have no irregulars after what he has eaten, it is usually have no tactical disadvantages if it is not a weakness for him.

Genius Intellect: Even before Korosensei gained his powers, he possesses a gifted mind which allows him to learn and understand complex knowledge in a matter of minutes. With his immense intelligence, he was able to single-handedly teach all the subjects and produce amazing results from the bottom of the barrel class of 3-E. Since gaining his speed, Korosensei has become hypercongnitive, and can process information thousands of times faster than the average human being. His incredible mentality combined with his speed also allows him to multitask on up to dozens of jobs at a time (teaching the entirety of Class 3-E individually and then some), all of which seemingly being done simultaneously.

  • Assassination: As the original God of Death, Korosensei was considered the world's best assassin prior to being betrayed by his disciple. As a result, Korosensei can combat nearly every assassination utilized by both Class E and professional assassins, showing to be extremely observant and stealthy at planning and execution.
  • Eidetic memory: Korosensei is deduced to have an eidetic memory, as he is able to store all that he has learned and use them to his advantage, which led to him being the strongest assassin in the world prior to his capture. In order to become an educator to class 3E, he has memorized all of the test books in Japan so as to be able to coach his students where their weaknesses lie.

Weaknesses

Because of his answer to the tentacles when they questioned him from within, here are the weaknesses Korosensei gained when he became the teacher to class 3E.

  1. When he tries to act cool, his weaknesses show.
  2. He is surprisingly quick to panic.
  3. He is petty.
  4. His punches are weak.
  5. Boobs (Natural weakness).
  6. He is humble and subservient to his superiors at work.
  7. He has no patience for wire puzzles. 
  8. He gets motion sickness.
  9. He can't sleep on a pillow other than his own.
  10. He worries about appearances.
  11. He can't handle hot food.
  12. Getting wet (Natural weakness).
  13. Juicy gossip.
  14. Hackneyed plot developments make him cry.
  15. He gets taken in by rumors. 
  16. Time right after molting (Natural weakness).
  17. Time right after regeneration (Natural weakness). 
  18. His body goes rigid when bathed in a special beam of light (Natural weakness).
  19. When he returns to normal after a serious situation, he gets embarrassed.
  20. He can only draw simple pictures.
  21. Heat fatigue.
  22. He is strict about poolside manner.
  23. He can't swim (Natural weaknesses).
  24. He likes to gossip.
  25. He is weak against the occult. 
  26. If he can't gather people, he feels worthless.
  27. Tone-deafness.
  28. He sucks at hiding.
  29. He gets carried away by official positions.
  30. Heart (Natural weakness).
  31. Not related but acts like a doting parent.
  32. Gets insurance to avoid getting hurt.
  33. He doesn't really know what "your own football" means.
  34. He sucks at reporting.
  35. He suffers from road rage
  36. Restructuring (Natural weakness).
  37. Grabbing all his tentacles at once makes him unable to move (Natural weakness).
  38. Unintentionally adding insult to injury.
  39. Completely oblivious to the mood in moments of high tension.
  40. Class 3-E students: Undeniably Korosensei's greatest weakness. Although students of 3-E class are subtly aware of this, only three students ever made actual attempts to exploit this factor: Karma Akabane, Nagisa Shiota (using themselves as baits), and Ryoma Terasaka (using Nagisa as a suicide bomber the first time, second unknowingly manipulated by Shiro into nearly drowning his classmates, but has redeemed himself since). Exploiting this weakness means one has no qualms of discarding lives of his/her classmates, and even their own.

Foibles

Korosensei hide certain things from students on his life which was revealed during Assassination Classroom Extras featuring Hotaru as Main Character of the series. Here are the foibles that Korosensei has for his life as an adult.

  1. Painfully narcissistic designs.
  2. His room resembles a dumpster.
  3. He only makes petty wagers.
  4. A bit of degenerate octopus.
  5. His purpose has shifted from using porn magazines to collecting them all at this point.
  6. Starts a nights off with Cassis and Orange.
  7. Takes forever to decide on appetizer.
  8. Really can't hold his liquor.
  9. Kind of like an old geezer.

In other media

J-Stars Victory VS

Korosensei is notably the only character from Assassination Classroom to appear as one of the playable characters in the anime crossover fighting video game J-Stars Victory VS.

Weekly Shōnen Jump Jikkyou Janjan Stadium

Korosensei appears as one of the playable characters in Weekly Shōnen Jump Jikkyou Janjan Stadium, a free anime crossover fighting mobile game for Android and iOS developed by Konami.

Quotes

  • (His vow to Aguri after her death) "So long as I have time... I will use this as a teacher. The students you watch over, I will watch them myself. No matter what, theses tentacles will not let them go."
  • (To Nagisa Shiota"The fact that I'm targeted by everyone is proof that I'm powerful, after all."[10]
  • (To Itona Horibe) "For Sensei, assassination is education. The sensei of the Assassination Classroom becomes stronger as he teaches."
  • (To his tentacles about what he wanted to be) "I want... to be weak."
  • (To his apprentice) "My dear student... may you graduate... in peace."
  • (To Gakuho on Valentine's day) "You didn't let emotions or background cloud your judgement... and evaluate me solely on my aptitude as a teacher. Such a proposal is the happiest report card you could have given me."
  • (To Class 3-E after telling his past) "If I'm going to be killed, it can't be at the hands of anyone else. I want to be killed by you."

Trivia

  • His name is a combination of the Japanese words korosenai and sensei. Which mean 'unkillable and 'teacher' respectively. So basically his name means "Unkillable Teacher". This name was given to him by Kayano, both in the original and in the RPG spinoff 'Koro-Sensei Q!'
  • Korosensei was called "Stupid Chicken Pervert Octopus" during class 3-E training using code names, rather than the code name he suggested, 'the imperial prince of fate of the eternal wind'.
  • It is revealed that Korosensei has never actually known his real name.
  • Korosensei is usually represented by a octopus due to his appearance of his head and tentacles. He has self awareness of it as he often draws octopus mascots while scoring exam marks and make jokes about octopus.
    • He also has a nature similar to octopus, as he is high intelligent for his survival skills.
    • His ability to regenerate his tentacles, healing others, bestowing wisdom, and octopi appearance is a reminiscent of the Akkorokamui.
  • In the popularity poll in Volume 12, Korosensei was ranked 3rd.
  • Korosensei is ambidextrous, being able to write/perform a task with either hands, and being able to work with both hands at the same time.
  • His motto is "Learning and killing are of one body."
  • According to Aguri, Korosensei is not Japanese.
  • His weaknesses for boobs was already seen when Aguri shows him her ogre themed thumb top which Aguri remark him as a pervert even before tentacle ask him for what he want to be making boobs as the only natural weaknesses.
  • When his tentacles asked him what he wanted, Korosensei's response was: "I want... to be weak".
  • His necktie is a present from Aguri Yukimura. Though, the crescent moon motif is his own design.
  • In chapter 136, he disguised as university professor.
  • Korosensei is potrayed by Jun Fukuyama, who previously potrayed an another manipulative protagonist, Lelouch vi Britannia's from Code Geass series.
  • He also is one of the most popular and recognizable anime heroes, in addition to being one of the primary members of the Shōnen Jump franchise. The reason why he is notably the only character from Assassination Classroom to become one of them is mainly because of some of his anime references that he has done.